


Tranquility

by wallstoothin



Category: Undertale (Video Game), 鬼滅の刃 | Demon Slayer: Kimetsu no Yaiba (Anime)
Genre: Breaking the Fourth Wall, Cute Kids, Flowey wish the baby would stop trying to pick him, Muzan is a meanie, Nezuko likes the underground, Parent Toriel (Undertale), Rokuta and Hanako want to pet all the dogs in the world, Takeo has street smarts, Tanjiro keep losing his brain cells via headbutting, Temmie go to collage, The Kamado siblings lives, The first chapter is very Meta, This AU would also work with digimon, prepare for family fun
Language: English
Status: In-Progress
Published: 2019-08-29
Updated: 2019-10-12
Packaged: 2020-09-29 14:11:28
Rating: Teen And Up Audiences
Warnings: Graphic Depictions Of Violence
Chapters: 4
Words: 3,850
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20437352
Author URL: https://archiveofourown.org/users/wallstoothin/pseuds/wallstoothin
Summary: After being demoted to such a position are you SURE you wish to go along with the story?>Yes>NoVery well.





	1. Terms and Conditions

**Summary for the Chapter:**

> Today we will sign a contract of no interference by willing continuing to the next chapter it would be assumed that you will abide by the terms and conditions. Failure to agree will end with some unfavorable "Punishment"

**Notes for the Chapter:**

> Please read this over again I fixed the timeline and plot by adding more bullshit in it.

Humanity has always been in wars one way or another, their **level** of monstrosity rises and the countries's sins piles on their descendant's back. But in every war there is a loser, a victor and a survivor. 

The survivor of the war between monsters and human, a child who escaped from the horrors of their elder and escape the punishment that his people have to face. The young monster was able to fall in love with a human - his people enemy. They fell in love with a young women who was always fascinated with their kind and their history. For exchange of protection the young monster told the girl stories, after love came children which made their own children.

Each of the decedents of the monster and the girl has some sort of power most invisible and weak, the most powerful of them all was Muzan Kibutsuji who created another war with the humans and lead to the creations of 'demons'.

Muzan cannot see the souls of people, he could not drag them out and attack them directly instead he hurts the human way, with teeth and blood and from that blood he creates a different kind of monster. One with no compassion and a need for human lives as a way to survive the cruel world that is the earth.

Meanwhile, the monsters who were locked away, continue to live, after all dying is not worth it after many of their kind sacrificed themselves so they can live, the monsters who organized themselves into a kingdom has lived out their lives in a normal way, towns were build and shops and restaurants were managed and the populations grew. 

Many years later the kingdom of monsters celebrated for their prince was born. A young boy, and then again the kingdom celebrated when the King and Queen adopted another child the same physical age as their prince. A young human child. The royal family lived on happily until an incident lead to the death of the two prince.

Since then the king has declared war on humanity once again since then six humans has walked into the land of monsters their body swept under the dirt and their souls dragged out and locked away in a glass jar. The angels from the monster's prophecy has not yet arrived and will not have another century, but until then...

* * *

Our story begins on a mountain. It has always began from the mountain.Where the seven great mage of the humans locked the monsters away into the underground and in order to avoid any greedy humans from taking hold of the monster and using them to take over humanity they change the entry way to different mountains around the world. Although Mt. Ebott is the entrance the eight humans fell into there are other places. The fact that many young souls fell into the same entry way is a mere coincidence. At least in the plane of that world for the world across the windows is ignorant of the other entrance. 

Now, we will ask you the player or little God wannabe (whatever you may call yourself) who have invested your souls and being into many different timelines of this universe to take a moment and stop/ Already has this timeline deviate from the others. This universe is no longer in your control. But then again, since when did you have full control.

This universe has already collided with another more different universe. One universe has no demon, the survivor was locked away in the underground with the rest of the people only for it's universe to change with the appearance of the last human soul where once again the universe is broken up into even more branches. One where they are able to see the sun again, one where they are are killed by the hands of a child with a knife (or a being behind the screen) and one in between where if they are spared force to continue their lives underground under another rule. 

The other is where the underground dies off and only the existence of demons remain, a universe where humans rise up to fight against the demons and where the fate of the world no longer rest on a player but on a young man with free will. 

This universe will focus on the main branch. You the being behind the screen will have no control what so ever and will be reassign as a **viewer **

**After being demoted to such a position are you SURE you wish to go along with the story?**

**>Yes**

>No

Very well.


	2. Cruelty

**Summary for the Chapter:**

> In which the author does not have the guts to murder children.

When his father died, he became the man of the house. But Tanjiro did not mind working hard for his family. In fact he have been doing that long before his father has passed since his father was very sick and was unable to move out of bed for a long period of time but his father was strong and Tanjiro admires him for it. 

He will carry his father's strength and carry his family on his back. After all he have so many things he want to do. He want to give his sisters fancy clothes and his brothers toys and candies and his mother, time to relax and not be stressed out all the time due to the family financial situation. It was near new year and once again Tanjiro was getting ready to head out into the snow to sell coal. It was their family main source of income and Tanjiro being the strongest and most able was the only one to do the job. As he load the basket of coal on his back his mother stops him. 

"Tanjiro." She said approach him with a towel. "Your face is all black, come over here." Tanjiro walked over to his mother who bend down and wiped the coal powder off his face. "Because it's dangerous when the snow is falling, it's ok that you don't go."

Tanjiro smile. His mother always say the same thing whenever the clouds settle in on the mountains. He know that it is because his mother cares for him and want him to be safe at home where she can watch over him. 

"I'll only go to sell a little charcoal, It's almost the new year and I want everyone to eat to their heart content." It was true his youngest brother was small for his age and Tanjiro believes that it's due to the lack of food. He want to be able to give his brother lots of food so he can grow stronger and taller. As always his mother gives the same responsive she give whenever Tanjiro refuse to stay home and go out to sell. 

"Thank you."

It was a simple response but whenever his mother says it his heart swells with integrity. The talk with his mother seem to have gather the attentions of his younger siblings who turn and face him with a big smile. 

"Ni-chan are you going to the village today?!" Shigeru asked excitedly.

"I wanna go to!" Hanako added. 

"EHHH" Takeo yelled out. It seem that he wanted to go as well but instead was expressing his disappointment of Tanjiro leaving.

His mother shook her head. "No, you can'twalk as fast as Tanjiro can."

"But Mom!"

"No." From the firm voice his mother gave out all the children can tell that there's no point in arguing with her. Her face soften "Because he cannot pull the cart today, you won't be able to rest if you get tired."

The children nod the younger two hugging their brother goodbye still mumbling their discontent of not being with their brother.

"Takeo, since you're the only one who ca, can you cut down some logs for firewood?"

Tekeo nodded swinging his axe on his back. "Alright. I thought that we could do it together today."

'So that's why he was upset earlier' Tanjiro thought as he decend the mountain and meet with his sister and his youngest brother.

"Onii-chan"Nezuko greeted with young Rokuta on her back wrapped around with warm cloth. " I just lulled him to sleep, because then he will cause an uproar."

"He just lonely because dad died." 

"It seems that everyone is stuck with you onii-chan."Nezuko agreed. It was true ever since their father passed the younest three has been trying to get Tanjiro to be with them all the time. They were sad and trying to cope he can tell. He want them to be happy again so today he'll work hard to get as much money as he can. After saying goodbye with his siblings,Tanjiro continue his journey to town and once he get their he's greeted with familiar and friendly faces. 

Tanjiro comes to the town often to either sell or buy things and since then he have been able to make friends with all the shopkeepers, because of so Tanjiro likes to help out around town especially for the elderly who cannot do somethings on their own.

"Well if it isn't Tanjiro-chan"

"Oi,I want to buy some charcoal."

"Thank you for fixing the door the other day."

"I want to buy some charcoal too!"

"Tanjiro ! Help me out!"

"Tanjiro can you help me carry my bags."

By the time he was done it was already dark and with all the coal gone and his money bag full it was time to return back to his home.

"Hey Tanjiro you're not going back at this time are ya?" 

Tanjiro turned around, it was the elder who lived in the bottom of the mountain. The old man would often allow the boy and his family rest and feed them sweet fruits in the summer.

"I have a keen sense of smell, it would be fine." 

The man shook his head. "I'll let you stay the night, come."

"But-"

"No buts. The oni will appear." 

Sabrou-oji san was not someone you should argue agaiainst. It was only one night and his mother will feel at ease if he stay over at someone the family trusts rather than moving at the mountain late at night. 

That night Tanjiro fell asleep hearing the tales of demons and demons slayers.

_Even thought it's scary it's alright since demons don't exists_

_But didn't grandmother say the same thing before she died?_

* * *

Tanjiro left the house early morning. It's almost new year after all and with the money he gather he want to be able to buy plenty of food to celebrate. He froze half way and sniff the air.

Iron, it smelled of iron and something else - blood. He smell blood from the direction of his home forcing his legs to move forward.

"Nii-chan!" 

Tanjiro stopped in his tracks, that was Shigeru's voice.

"Onii-chan over here!" 

And that was Hanako.

He finally found his siblings hiding behind some trees each with tears in their eyes and fear on their face they were all staring at something on the floor.

His younger sister Nezuko sleeping on the floor with a large gash on her arm.

**Notes for the Chapter:**

> Age of the Kamado kiddos
> 
> Oldest (First son)- Tanjiro age 13  
2nd child (First daughter) Nezuko age 12  
3rd child (2nd son) Takeo age 10 (almost 11)  
4th child (2nd daughter) Hanako age 6 (almost 7)  
5th child (3rd son) Shigeru age 5  
6th child (4th son) Rokuta age 2
> 
> Although none of the other children have age I have to guess based on their action.  
Takeo is mature enough to cut wood on his own but still want the attention of his big brother (wanting to cut wood together)
> 
> Hanako and Shigeru seem to not do any work and get tired easily, they seem to also whine and want to cling onto Tanjiro
> 
> Rokuta is young enough to be easily carried by Nezuko but old enough to understand that their father is dead (or at least knows that he's never coming back)


	3. Lurking

**Summary for the Chapter:**

> No matter what happen the Kamado children will always love each other.

**Notes for the Chapter:**

> This is where the weird timey-whimey stuff happens, something I should mention now is that time pass differently in the underground and with monsters in general. 
> 
> For example, there is no sun meaning there is no true night and day. The "Sunlight" in judgement hall is a simulation to be able to "tell" time in the underground. That does not mean that a day is equivalent to 24 hours. A year and a month is still roughly the same number but since time passage is different it is much "longer" than the surface. 
> 
> There is also the matter of age, after consuming a lot of monster foods the passage of time in your body slows. Meaning that you age slower. The same is for monsters since their body is literally magic so even if let say Sans say he's 25 he is actually over a century or so old. I'm willing to answer any question so please don't hesitate to ask.

Why is his sister lying on the ground in a pool of blood. Where is his mother?

He wanted to ask so many questions but he know that if he don't get Nezuko to a doctor soon she will die.

All of his other siblings were crying, Tanjiro wanted to cry too. But he was the oldest and he need to keep it together for their sake.

His heart is filled with integrity. 

Tanjiro quickly threw the empty coal basket at Takeo. "We're going to go find a doctor for Nezuko, but Rokuta in the basket."

"Nii-san....mom she.."

Tanjiro figures his mother died or at least something bad happened to her most likely to protect his siblings.

"I know." He admits. "I know that you all must be hurt and scared." He eyed the bruises on his siblings. "But we need to move on and get help, I'll carry Nezuko on my back and Takeo will carry Rokuta. Hanako, Shigeru can you both walk."

The younger two looked at him and nodded.

"We can do it."

"We'll walk for nee-chan"

The five quickly set out soon after, Tanjiro in the front decending the mountain in a fast pace and his siblings are slowly behind.

"Don't worry Nezuko, your family is going to save you." He mumbles jumping over a patch of ice. He was close to the town, he was pretty sure that the elder who live at the base of the hill would help him or at least let Nezuko and the other stay at his house while he go and find a doctor. 

Tanjiro stopped at he felt movement from behind him. 

"Nii-chan, nee-chan is waking up!" Takeo called out. 

Nezuko slowly pushed himself off from his back landing on her feet. 

"Nezuko, are you alright, you should move around with your injuries." 

Tanjiro took a deep breath taking in the new smell, his hand inching towards the ax hanging on his belt and in front of his eyes his younger sister change, her veins pulsing and visible her normally ruby eyes turning as pink as her kimono and her normally straight teeth turning sharp. All of this was in front of Tanjiro and only one world come into his mind.

'Oni'

But that can't be, his sister is human, she have been born human and have been raise as one. But the rest of the kids did not know she was a demon, if they did they would have been afraid of her instead of trying to get her help meaning that someone probably did this to her and whoever hurt Nezuko most likely killed. 

Nezuko launch forward and Tanjir blocked by using the wooden part of the ax as a bar against her sharp fangs.

"Nii-"

"Takeo stay back, there's something wrong with Nezuko." He shouted. He was slowly getting pushed back by the younger girl to the point where they are both on the floor. 'Is she getting heavier' He knows that his sister is still there, her faint smell of cherry is still on there covered by another strange smell.

"Try your best Nezuko ! Try you best and hold it off. You turn into an oni but you need to keep it together.I know you can do it." 

Tanjiro watched as tears gathered in the younger girl's eyes, he can also feel tears gathering in his own eyes as well. 

"Nii-chan look out !"

Tanjiro rolled out of the way pulling his sister along as the two tumble into the snow. Once he get's a grip he carefully sat up with his sister. In front of him was a stranger wearing mis-matched kimono and a western looking uniform underneath. His siblings hiding behind Takeo who was hiding behind a tree. From the way the man's katana is pointing it is clear who his target is. 

"Why did you protect it."The man asked. It was unclear if the man was confused or annoyed.

"She's - she's my sister, she's my younger sister."

Nezuko screeched trying to get away from Tanjiro's grip. The older boy held a steady grasp trying to not let her get away.

"That thing is your sister?"

And in a flash Nezuko was ripped away from his grip and was held tightly by the man.

"Don't move."

The other children froze in their spot watching in horror as their sister try to escape.

"My job is to kill demons, of course I'm going to decapitate your sister."

"Please don't! She haven't killed anyone ! I don't know whyshe's acting like that. " Tanjiro plea.

"It's simple if you bathe an open wound in demon;s blood you become one. This is how their man eating number increase."

"But she haven't eaten anyone !"

Takeo's ax flew pass him and heads towards the stranger. In reflex the man moved out of the way loosing his grip with his captive. Tanjiro grabbed Nezuko's hand.

"Onii-chan, run!' Shigeru shouted and the siblings all started to run up the hill. It was clear that the man was chasing them as well. The now demon was still trying to escape but Tanjiro still held her as tight as he could. He's not going to let her go again.

"Onii-chan." Hanako sniffed her little legs filled with blood and bruises from running all night. "I can't...I can't"

Using his other free hand Tanjiro held his other sister's hand while Nezuko watch in fascination. "We have to keep going." 

The group continue to run until they come across a large hole, the man was already right behind them there was no time to move to the side. The younger siblings all stood behind Tanjiro who held a stick in his hand. 

The stranger stopped in front of the siblings. "She's going to kill you all." He said with utmost certainty.

"Nee-chan loves us!" Rokuta called out from inside the basket on Takeo's back glaring with all the might a two year old can give. "And you're a bully !"

Out of every words that was said the careless words of a toddler seem to have stuck. The man then took a step forward and the group took one too many step back as Takeo, Shigeru and Rokuta each gave out a large scream their body heading towards the ground under the hole, Tanjiro automatically reached out letting go of Hanako who held held on to Shigeru's hand but trying to carry the weight of two people weight him down as he felt his feet dragging on the floor and with a large crack the piece of earth broke off. The remaining siblings cried out as the siblings plunges into uncertaintly.


	4. Chapter 4

The flowers that Rokuta laid on was soft, he didn't know that flowers can be this soft since most of the flowers he seen are small and on tall trees. The young child sat up and looked around, his knees were swollen and painted in colors of blue and black, strange his skin never change colors like these before.

He looked over to the side, right beside his legs was a broken basket that Rokuta have been riding on his brother's back, the same brother that was waking up from his forced nap, forcing himself to stand, the toddler walked over to his brother.

"Takeo-nii." He cried out. He want to be with his much older brother and sister but they are currently sleeping and mother say he should not bother them when they are sleeping.

But mother is not here with them, just like father.

Rokuta felt the need to **voice** out his heart and feeling.

Hanako and Shigeru started to walk over to Takeo as well. Takeo grabbed them all and hugged them.

And the cried.

And cried

And cried.

Their older brother and sister still won't wake up.

"Oh my child are you alright...children?"

A voice in the distance, the younger four children looked over to where the sound is coming from. It was a strange being her body seem to be like a human beside for the fact that she also looked like some sort of goat.

Takeo gulped, this stranger might be the same as the last and try to murder Nezuko again! Tanjiro is still unconscious so as the oldest at the moment it was Takeo's job to protect everyone, with** bravery** in his heart he stood up and glare at the strange creature. "Stay away! Get away from us!"

The monster step closer. "Do not worry children for I bring you no harm. My name is Toriel, the caretaker of the ruins. "

He have never heard of goat like monsters in school or in the story book. But then again Rokuta is only two and he don'nt know what 'Caretaker of the ruins' means.

The stranger continued ignoring his older brother's threat. "The ruins is my home, I wander here everyday to see if a human falls in. I was lucky to find you all here before another monster did. Why don't you come with me, so we can treat your brother and sister."

Shigeru sniffed rubbing snot all over his sleeves. "Takeo-nii, maybe we should go, the monster said she can help us and Nii-chan and Nee-chan." 

Takeo's ruby eyes darted back and forth between his older sibling and the monster. "Ok, Toriel-san. We'll go with you." 

The siblings with the help of Toriel then carried their siblings across the ruins. There were plenty of traps and strange puzzle, but Toriel told the group they will come back another day, Rokuta as the youngest was not allowed to help, the only thing he was allowed to do is hold onto Toriel's purple robes as she guide them. His foot hurt more than it ever did before, normally he would go to his mom or one if his brothers and sisters but mom was not here, the same way like dad. They left mom back home. 

When can they go home?

* * *

The group left Tanjiro and Nezuko back in the strange room. The 'house' was different from their little wooden hut, but the warm atmosphere was still here. Toriel was very helpful, she healed everyone with a strange green light. She explained it was magic. Hanako hopes she can do the same one day. She also fed them something strange call pie. It was sweet and very filling. Hanako never ate anything like this before!

She concluded that Toriel must be very rich to be able to afford such food. Afterwards they all had a bath! Hanako, Shigeru and Rokuta all fit in the strange bucket and even though there was no water before all the sudden there was and it was warm and clean (but after it was filled with pie filling from Rokuta's messy eating.) They were forced to part way with their Kimono though, it was dirty and ripped apart but Hanako can fix it. Her nee-chan and nii-chan taught her how! So she begged Toriel to allow them to keep it it, and in exchange they had to wear the strange clothing that Toriel has made for them. 

It was called a sweater, it was warm and fuzzy with thick material. It was much warmer than wearing layers. What was better is that the color matched with her old kimono. It was a striped sweater with two shade of pink, the lighter shade was used as the background while the shade as two stripes across the middle. Takeo has a green and black one while Shigeru has pale green and yellow. 

Rokuta has more stripes than other, a nice royal blue with a slightly lighter shade. When Shigeru asked why he had more stripes, Toriel said that it was to show that he was younger. In the monster community all children wears strips but thoes with more strips show that they need better supervision from the adults. It was normally reserve for younger and those monster who have a tendency to wander off. 

It made sense she suppose.


End file.
